In a flat cutting press which effects cyclic cutting of a continuous web, printed or not, of a material such as cardboard, this web is generally continuously delivered upstream from a reel. As the flat cutting press is a machine which necessitates a momentary stop of the advance of the web of material, during the cutting operation, there is produced, due to the continuous supply, an accumulation of the material to be cut, upstream of the cutting press. In order to be able to accumulate the length of web delivered continually upstream, whilst a downstream part of this web is in stopped position in the flat cutting press, various devices have already been designed which store the excess length of the web in the form of a loop of variable length which is either free or controlled by passing beneath a mobile cylinder, called "oscillating cylinder". This loop lengthens during stop of the cutting press and it shortens as soon as supply of the cutting press resumes, with a view to a subsequent cutting operation, these operations taking place cyclically.
A supply device of this type, which is described in Patent FR-A-2 618 770, further comprises, between the mobile cylinder controlling formation of the loop of variable length, and the flat cutting press, a suction cylinder, over part of the periphery of which the web to be cut passes before entering the press. This suction cylinder is hollow, its lateral wall is pierced with holes and inside the suction cylinder is housed a suction box which is connected to a source of vacuum and which is in contact with a part of the inner surface of the hollow suction cylinder. The position of the suction box and its extension in the direction of rotation of the suction cylinder correspond to the zone in which the web is in contact with the outer surface of the suction cylinder. This suction cylinder is, furthermore, driven in rotation at a constant peripheral speed which is greater than the speed of supply of the web upstream. Such a suction cylinder serves to maintain the web under tension and it ensures acceleration of the web when, after a cutting operation in stopped position, this web is again introduced inside the cutting press.
In such a known supply device, the inner box of the suction cylinder is permanently subjected to a constant depression created by the source of vacuum. This results, during the phase of stop of the web inside the cutting press, in a certain instability of this web on the suction cylinder, since this cylinder is permanently rotating and its holes which pass beneath the web, then immobilized, attract, due to the depression present, zones of the web which move thereon. Furthermore, as the depression prevailing in the suction box is chosen to be sufficiently high to obtain a good acceleration of the web, when the latter must be advanced in the cutting press, there results a relatively high pressure of application of the web immobilized on the outer surface of the suction cylinder in rotation, detrimental to the quality of certain materials when a very high speed is attained.
It is an object of the present invention to overcome these drawbacks.